Summary

The piston of linear compressors experience low transversal loads and the refrigerant gas in the piston - cylinder clearance can be used to form an aerostatic bearing. Despite the reduction of friction in the bearing , the gas flow in the piston - cylinder clearance generates losses that decrease the compressor efficiency. The present dissertation reports a model developed to evaluate such losses and their effects on the volumetric and isentropic efficiencies for an oil - free linear compressor. The transient flow in the gap is simulated with a commercial code based on the finite volume method, whereas the compression cycle in the cylinder is characterized via a lumped model. The attention is focused on the flow losses and other inefficiencies , associated with gas superheating inside the cylinder and with suction and discharge processes , are not included in the analysis . Different design parameters were considered in the analysis and the cylinder and the piston are assumed to be concentric during the compression cycle . It was found that the compressor efficiency is reduced when the clearance dimension and pressure ratio are increased , but the opposite effect was observed in relation to the operation speed.

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